Cathode ray tube focusing and conveying system

ABSTRACT

A COLOR PICTURE TUBE OR OTHER CATHODE RAY TUBE EMPOLYING A PLURALITY OF ELECTRON BEAMS INCLUDES A SINGLE ELECTRON GUN HAVING ONE OR MORE CATHODES EMITTING ELECTRONS FORMED INTO THE PLURALITY OF BEAMS WHICH ARE MADE TO CONVERGE OR CROSS EACH OTHER SUBSTANTIALLY AT THE OPTICAL CENTER OF AN ELECTROSTATIC FOCUSING LENS BY WHICH THE BEAMS ARE FOCUSED ON THE ELECTRON-RECEIVING SCREEN OF THE TUBE, WHEREBY TO AVOID SPHERICAL ABERRATION AND/OR COMA. WHEN THE BEAMS FOCUSED ON THE ELECTRON-RECEIVING SCREEN ARE ALL TO CONVERGE AT A COMMON POINT ON SUCH SCREEN, AN ELECTROSTATIC OR MAGNETIC DEFLECTION DEVICE ACTS ON THOSE BEAMS WHICH DIVERGE AFTER PASSING THROUGH THE LENS-LIKE FOCUSING SYSTEM.

Sept. 11, 1973 Original Filed Jan. 12,

FIG 1.

FIG. 2.

FIG. 3.

FIG. 4.

SUSUMA YOSHIDA ET AL CATHODE RAY TUBE FQCUSING AND CONVEYING SYSTEM 3Sheets-Sheet l A K: B

K r 82) d 18 Sept. 11, 1973 SUSUMA YOSHIDA ETAL Re. 27,751

CATHODE RAY TUBE rocusmc AND CONVEYING SYSTEM Original Filed Jan 12,1968 3 Sheets-Sheet 1 FIG. 5. K2

FIG. 6.

L 5 1 5K 4 B1 1 do 2 O 2 5 do 83 ;KB 52 A FIG. 8.

P 11, 1973 SUSUMA YOSHIDA ETAL Re. 27,751

CATHODE RAY TUBE FOCUSING AND CONVEYING SYSTEM 5 Sheets-Sheet 3 OriginalFiled Jan l2 1968 mm \& E252 Q flw @2 1 92 mma! H m wmnwlwmwwwwwfim MH 24i. V H mm P I k g m m8 20: Q8 1. HH \EQN oov 3 0 en 8 Q oow I 3 0United States Patent Oflicc Re. 27,751 Reissued Sept. 11, 1973 27,751CATHODE RAY TUBE FOCUSING AND CONVERGING SYSTEM Susumu Yoshida and AkioOhgosbi, Tokyo, Seurl Miyaoka, Fujisawa, and Yoshiharu Katagiri, Tokyo,Japan, assignors to Sony Corporation, Tokyo, Japan Original No.3,448,316, dated June 3, 1969, Ser. No. 697,414, Jan. 12, 1968.Application for reissue Oct. 13, 1971, Ser. No. 188,847

Int. Cl. H01j 29/56, 31/20 US. Cl. 313-69 C 32 Claims Matter enclosed inheavy brackets [II appears in the original patent but forms no part ofthis reissue specification; matter printed in italics indicates theadditions made by reissue.

ABSTRACT OF THE DISCLOSURE A color picture tube or other cathode raytube employing a plurality of electron beams includes a single electrongun having one or more cathodes emitting electrons formed into theplurality of beams which are made to converge or cross each othersubstantially at the optical center of an electrostatic focusing lens bywhich the beams are focused on the electron-receiving screen of thetube, whereby to avoid spherical aberration and/or coma. When the beamsfocused on the electron-receiving screen are all to converge at a commonpoint on such screen, an electrostatic or magnetic deflection deviceacts on those beams which diverge after passing through the lens-likefocusing system.

This invention generally relates to cathode ray tubes, and moreparticularly is directed to improvements in color cathode ray tubes ofthe type in which a single electron gun is provided for emitting aplurality of electron beams to produce a color picture, for example, asin color television receivers.

Existing color picture tubes are usually of the multigun type andinclude three independent electron gun emitting respective electronbeams which are modulated by corresponding color signals and acted uponby a grid system so as to be focused on a collector or electronreceivingscreen which may be simply a phosphor or luminescent screen or aphosphor screen with a perforated electrode or shadow mask in frontthereof. The three electron guns have to be aligned with respect to eachother so that the emitted electron beams converge at theelectron-receiving screen. Such color picture tubes of the multi-guntype are disadvantageous in that it is difficult to obtain and maintainthe precise alignment of the three electron guns required for theconvergence of their beams on the electron-receiving screen and anymisconvergence of the beams causes deterioration of the quality andresolution of the color picture that results. Further, when using threeindependent electron guns to produce the beams, the color picture tubeis necessarily costly and, by reason of the space required for the threeguns, the possible miniaturization of the tube is correspondinglylimited.

In an attempt to avoid the above mentioned disadvantages and limitationsof the existing color picture tubes of the multi-gun type, it has beenproposed to provide a color picture tube of the single-gun, plural-beamtype in which a single electron gun emits three beams from either threerespective cathodes or a single cathode, and the three electron beamsare passed through a lens-like focusing system, so as to converge at theelectronreceiving screen. However, in the tubes of the singlegun,plural-beam type heretofore proposed, no more than one of the electronbeams passes through the lens-like focusing system at the optical axisof the latter, and the beams that pass through the focusing system at adistance from the optical axis are subject to coma and sphericalaberration. By reason of such coma and spherical aberration and theconsequent deterioration of the quality of the color picture thatresults, color picture tubes of the single-gun, plural-beam type havenot enjoyed any wide-spread use.

Accordingly, it is an object of this invention to provide a cathode raytube of the single-gun, plural-beam type which is free of the abovementioned disadvantages characteristic of tubes of that type aspreviously proposed, and which is particularly suited to serve as acolor picture tube for producing color pictures of high resolution andbrightness.

Another object of this invention is to provide a cathode ray tube,particularly a color picture tube, which is of the single-gun,plural-beam type and can be relatively easily manufactured even whenminiaturized to a considerable degree.

Still another object of this invention is to provide a color picturetube of the single-gun, plural-beam type in which correction forconvergence can easily be etfected.

In accordance with an aspect of this invention, a cathode ray tubeadapted for use as the picture tube of a color television receiver isprovided with a single electron gun including a cathode structureemitting electrons which are formed, as by a grid structure, into aplurality of electron beams, and such beams are made to convergesubstantially at the optical center of a lens-like, electrostaticfocusing means which is common to all the beams and focuses the beams onthe electron-receiving screen, whereby the introduction of opticalerrors such as spherical aberration and/or coma is avoided.

In cases where the electron beams are emitted parallel to each other,the convergence of the beams at the optical center of the lens-likefocusing means in accordance with this invention is effected byauxiliary electrostatic lens means located between the grid structurewhich forms the electron beams and the focusing means.

Further, when it is desired that the beams focused on theelectron-receiving screen should be converged at a common point on thescreen, the beams which diverge from the lens-like focusing means areacted upon by either electrostatic or magnetic deflection means locatedbetween the focusing means and the screen.

The above, and other objects, features and advantages of this invention,will become apparent from the following detailed description ofillustrative embodiments which is to be read in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagrammatic view illustrating the optical equivalent oranalogy of a three electron gun system, as in a conventional colorcathode ray tube;

FIGS. 2 and 3 are similar diagrammatic views of the optical equivalentor analogy of a singlegun, plural-beam system, as previously proposed;

FIG. 4 is a diagrammatic view of the optical equivalent or analogy ofstill another single-gun, plural-beam system as previously proposed;

FIG. 5 is a similar diagrammatic view showing the optical equivalent ofan electron gun according to an embodiment of this invention;

FIG. 6 is a view similar to that of FIG. 5, but illustrating an electrongun according to a second embodiment of this invention;

FIGS. 7 and 8 are diagrammatic views of the optical equivalents of stillother embodiments of this invention;

FIG. 9 is a schematic longitudinal sectional view of an electron gun inaccordance with the embodiment of this invention represented by theoptical analogy of FIG. 5;

FIG. 10 is an end view of the gun shown on FIG. 9;

FIG. I] is an enlarged elevational view showing details of first andsecond grids of the electron gun according to the embodiment of thisinvention shown in FIG. 9;

FIG. 12 is a sectional view taken along the line 1111 on FIG. 11;

FIG. 13 is a schematic, axial sectional view of a chromatron type colorcathode ray tube embodying the present invention; and

FIGS. 14A and 14B are respectively a plan view and an end view ofmagnetic deflection means which can be used for converging the electronbeams in a cathode ray tube according to this invention.

In order that the electron gun for a cathode ray tube according to thepresent invention may be better understood, the principles and featuresof conventional electron guns employing the triple-gun system and thesinglegun, triple-beam system, respectively, will first be described indetail with reference to FIGS, 1 to 4.

FIG. 1 shows the optical equivalent or analogy of a conventional systememploying three independent electron guns A A, and A;;. In such system,there are provided three independent beam generating sources K K and Kemitting three beams B B and B respectively, which are focused onto anelectron-receiving or phosphor screen S through separate main lenssystems L L and L respectively. With such an arrangement, however, thethree independent electron guns A A and A which need to be accommodatedin the neck portion of the tube envelope obviously restrict the extentto which the diameter of the neck portion can be reduced. Further, ifthe effective diameter of each electron gun is limited so as to permitthe accommodation of the three guns in a neck portion of reasonablediameter, the outer portions of each beam necessarily pass through partsof the respective main lens system L L or L, which are spacedsubstantially from the optical axis thereof whereby spherical aberrationresults with the consequence that each beam impinges on the screen S asa relatively large spot, as indicated at the right-hand side of FIG. 1,and high resolution cannot be obtained. It will also be apparent that,in using three independent electron guns, it is inherent thatdifficulties will be encountered in obtaining and maintaining theprecise alignment of the guns necessary for converging the beams B B andB at screen S.

FIG. 2 shows the optical equivalent of a conventional single-gun,triple-beam system in which the single electron gun A includesequivalent beam generating sources K K;- and K spaced from each other bythe distances d and from which three beams B B and B are emitted inparallel to each other so as to pass through the common main lens systemL and be converged by the latter on the screen S.

Whether the electron gun system of a color cathode ray tube is of thetriple-gun type (FIG. 1) or of the single-gun triple-beam type (FIG. 2),it is necessary that the three electron beams be converged at an angleof A6 between the center beam (B in the drawing) and each of the otherbeams so that the three beams cross or intersect each other at theposition of a mask or grid provided in front of the phosphor orluminescent screen and are thus made to land or impinge on respectivecolor dots or stripes which are adapted to produce different color lightrays.

In order to meet the foregoing requirements with respect to the angle A0in the single-gun, triple-beam system, it is essential that the threebeams B B and 3;; be spaced apart from each other by the substantialdistance d when they pass through the main lens L. Thus, beams B and 8;,pass through portions of lens L which are spaced substantially from theaxis of the lens L by the distance d, so that the beam spots on thescreen S are deformed, as shown at the right-hand side of FIG. 2, due tocoma as well as to spherical aberration. In the case shown on FIG, 2,the focusing of the beams is adjusted to achieve perfect convergence atthe screen S. This inevitably decreases the focusing elfect imparted toeach beam. Thus, the beams are under-focused so that the resulting beamspots are enlarged, as is apparent at the right-hand side of FIG. 2. 0nthe other hand, if the focussing voltage is adjusted to sharply focusbeam B on screen S, this causes the beam spots B B and B on the screen Sto be scattered, as shown on FIG. 3. Therefore, special means have to beprovided to converge or superimpose the beam spots which are thusscattered. However even in that case the beam spots B and B are deformeddue to coma, as shown on the right-hand side of FIG, 3.

In an attempt to satisfy the contradictory conditions of focusing thethree beams on screen 8 and of converging the three beams at the screen,it is conceivable that the three beams B B and B could be emitted from abeam generating source K in three different or angularly displaceddirections so as to be spaced apart from each other a distance d at theposition of the main lens L, as illustrated on FIG. 4. Although theabove two conditions can thus be simultaneously satisfied with onlynegligible spherical aberration, nevertheless the side beam spots B andB are blurred due to the coma, as shown at the right-hand side of FIG.4, since the side beams pass through the main lens L at positions spacedfrom the axis of the lens by the distance d.

It will be seen from the above that cathode ray tubes employing thesingle-gun, triple-beam system as previously devised or proposed fail tosatisfactorily meet the three-beam spot focusing condition and thethree-beam spot converging condition and therefore have not been put topractical use as yet.

In the following detailed description of illustrative embodiments ofsingle-gun, plural-beam systems according to this invention, particularreference is made to the use thereof in color picture tubes, but it isto be understood that the described single-gun, plural-beam systemsaccording to this invention can be applied to any other cathode raytubes in which plural electron beams are required.

In the system according to this invention, as illustrated by its opticalequivalent or analogy on FIG. 5, a single electron gun A includesequivalent beam generating sources K K and K which are located on astraight line in a plane substantially perpendicular to the axis of theelectron gun and spaced apart from each other by a distance d These beamgenerating sources K K and K emit three electron beams B B and Brespectively, which are refracted by means of a common auxiliary lens Lso as to be converged substantially at the optical center of a main lensL. Thus, the three beams B B and B are made to cross each other at theoptical center of the main lens L and then emerge from the lens L indivergent directions. Subsequently, the beams B and B which diverge fromthe optical axis and from the beam B lying on such axis, are deflectedtoward the center beam B by means of convergence deflectors F and F,provided between the electron-receiving screen S and the main lens L andspaced from the latter by a distance 1, so that the three beam spots B Band B on the screen are converged or superimposed on each other.

With the arrangement of FIG. 5, therefore, very small beam spots can beobtained since all three beams B B and B pass through the center of mainlens L, and thus the focused beam spots are prevented from being blurreddue to the coma and spherical aberration. Consequently, a picture with ahigh resolution can be produced. Furthermore, utilization of thedeflectors F and F advantageously facilitates the dynamic convergencecorrection with respect to the three beams. Although FIG. 5 representsthe deflectors as being of the electrostatic type, they may be of themagnetic type as hereinafter described in detail.

FIG. 6 shows the optical equivalent of a cathode ray tube according to asecond embodiment of this invention in which a single electron gun Aincludes beam generating sources K K and K arranged on an arcuatesurface having its center at the optical center of a main lens L, andbeing spaced from each other by the straight distance d In thisembodiment, the auxiliary lens L' of FIG. 5 is omitted, as thearrangement of the sources K K and K; on the described arcuate surfacecauses the three beams B B and B to cross each other at the opticalcenter of the main lens L, as in the embodiment shown on FIG. 5.Deflectors F and F are provided along the paths of the two beams B and Bwhich cross each other within lens L and then follow diverging emergentpaths, and such deflectors cause the beams B and B to converge andintersect the beam B; at the screen S. Thus, good resolution of thepicture can be obtained in the same manner as described above inconnection with FIG. 5.

Although the beam generating sources K K and K in FIGS. 5 and 6 arespaced apart from each other by a distance d or d along a straight line,it is possible to arrange these beam generating sources at the verticesof an equilateral triangle, in which case deflectors, as at F and F maybe provided for each of the three beams or for only two of them.Preferably, the beam generating sources are arranged along a straightline, as shown. The reasons are that, with such preferred arrangement,the effective distance over which the beams are spaced apart from theoptical axis can be minimized, the dynamic convergence correction can beeasily effected, and asymmetrical convergence of the three beam spots onthe screen can be prevented.

In the embodiments of this invention described above with reference toFIGS. 5 and 6, the three beams B B and B are made to converge at thescreen S. However, it is also possible to omit the deflectors F and P;so that the three beams 13;, B and B cross each other at the opticalcenter of the main lens L and thereafter continue along divergent pathsso as to strike the screen at three difierent positions spaced from eachother by a predetermined distance, as shown on FIGS. 7 and 8 whichcorrespond to FIGS. 5 and 6, respectively. With the arrangements ofFIGS. 7 and 8 the three beam spots on the phosphor screen are notaffected by the spherical aberration and coma of the main lens, so thatsuch beam spots need not be deformed as shown on FIGS. 2 to 4. When thebeam spots are spaced apart on screen S, time ditferences correspondingto the three beam spot positions are imparted to the video signalsmodulating the three beams, thereby achieving correspondence between thethree pictures produced on the phosphor screen by the three beams.

A particular example of the structure of an electron gun A correspondingto the optical analogy of FIG. 5 will now be described with reference toFIGS. 9 and 10 in which a cathode K constitutes the electron beamgenerating sources K K and K A first control grid G which, as shown onFIGS. 11 and 12, comprises three grid members G11, G and G is supportedin close, opposing relationship to the electron-emitting end surface ofcathode K. The three grid members G11, G and G have apertures g g and grespectively, arranged on a straight line. A common grid G having threeapertures g ggg and g formed therein is mounted in opposing, adjacentrelationship to the grid G with the apertures g ggg and g thereof inalignment with the apertures g g and g respectively. The grid G may becupshaped to include a disk 1 (FIGS. 11 and 12) having the apertures g gand g therein at spaced locations on a diametrical line 1111 and acylindrical side wall 2 extending from the periphery of disk 1 in theaxial direction away from grid G Arranged in order following the grid 6;in the direction away from control grid G are successive, open-ended,tubular grids or electrodes G G and G (FIG. 9).

Electrode G includes relatively small diameter end portions 3 and 4 anda larger diameter intermediate portion 5, and is supported with its endportion 3 extending into cup-shaped grid G and spaced radially from sidewall 2 of the latter. Electrode G includes end portions 6 and 7 of adiameter larger than that of end portions 3 and 4 of electrode G and anintermediate portion 8 of still larger diameter, and electrode G ismounted so that end portion 4 extends into, and is spaced radiallyinward from end portion 6. Electrode G includes end portions 9 and 10 ofa diameter smaller than that of end portion 7 and an intermediate,relatively larger diameter portion 11, and electrode G is mounted sothat its end portion 9 extends into, and is spaced radially inward fromend portion 7 of electrode G The several electrodes G G and G grids G Gand cathode K are all assembled together in the above described relationby means of suitable supports 12 of insulating material. Further, agetter chamber GT is provided around the end portion 10 of electrode GIn operating the electron gun of FIG. 9 appropriate voltages are appliedto grids G, and G and to electrodes G G and G For example, a voltage of0 to 400 v. is applied to the grid G (G G and G a voltage of 0 to 500 v.is applied to the grid G a voltage of 13 to 20 kv. is applied to theelectrodes G and G and a voltage of 0 to 400 v. is applied to theelectrode 6,, with the voltage of cathode K as the reference. Therefore,the voltage distributions with respect to the grids and electrodes G toG and their lengths and diameters are substantially identical with thoseof a unipotential-single beam type electron gun which includes a firstsingle grid member and a second grid provided with a single aperture.With the applied voltage distribution described above, an electron lensfield is established between grid G and the end 3 of electrode G whichcorresponds to the auxiliary lens L of FIG. 5, and an electron lensfield corresponding to the main lens L of FIG. 5 is formed at the axialcenter of electrode 6.; by the electrodes G G and G In one operation ofthe electron gun, bias voltages of v., 0 v., 300 v., 20 kv., 200 v., 20kv., are applied to the electrodes K, 6,, G G G and G respectively.

In order to cause convergence of the beams B and B; which emerge fromelectrode G along divergent paths, the electron gun of FIG. 9 furtherhas deflecting means F that includes shielding plates P and P providedin spaced opposing relationship to each other and extending axially fromthe free end of electrode G Deflecting means F further includesconverging deflector plates Q and Q, which are outwardly convexly bentor curved, for example, and are mounted in spaced opposing relation tothe outer surfaces of shielding plates P and P, respectively. The platesP and P and the plates Q and Q are disposed so that the beams B B and Bpass between the plates P and Q, between the plates P and P and betweenthe plates P' and Q, respectively. A voltage equal to that imparted tothe electrode G is applied to the plates P and P, and a voltage lowerthan that applied to the plates P and P by 200 to 300 v. is applied tothe plates Q and Q. Thus, deflecting voltage differences are appliedbetween the plates P and Q and between the plates P and Q whichrespectively constitute the deflectors F and F; of FIG. 5 and areadapted to impart the deflecting action to the beam B and Brespectively, as described above in connection with FIG. 5.

Thus, the three beams B B and B emanating from the cathode K are made topass through the apertures g g and g of grid members G G and G and aremodulated with three different signals applied between the cathode K andthe grid members G G and G The beams B B and B pass through the commonauxiliary lens L which is formed mainly by the grid 6 and electrode Gand cross each other at the center of the main lens L which isconstituted mainly by the electrodes G G and G Then the beams B B and Bpass between the plates Q and P, between the plate P and P and betweenthe plates P and Q respectively, after having left the electrode G Sinceplates P and P are at the same potential, beam B is not deflected, butthe beams B and B which emerge from lens L along divergent paths aredeflected, so that the three beams B B and B are made to converge at apoint on the electron-receiving screen.

In the embodiment described above with reference to FIGS. 9 and 10, itis necessary that signals be separately applied to the three gridmembers G G and G constituting the first grid (3, since the three beamsources K K and K are provided on the single cathode K. To meet suchrequirement, the three rectangular plate-like grid members G 1, G and (iwhich are respectively formed with the apertures g g and g haveconnector tabs 13 extending therefrom to receive the signals formodulating the electron beams independently of each other.

In order that the positional relationship of the apertures g g and g ofgrid members G G and G will be precisely predetermined, and that theapertures g g and g will be concentrically aligned with apertures g gand gag of the second grid G with a predetermined distance D beingmaintained between the second grid G and the first grid members G G andG two ceramic insulator pieces 14, each having a thickness D, areinterposed between grids G and G Each of these insulator pieces 14 has aconductive layer covering an entire surface thereof, as by metallizingthat surface. Also, three conductive layers M M and M extend across thewidth of the opposite surface of each insulator piece in uniformlylongitudinally spaced relationship to each other. The insulator pieces14 are disposed on the disk of the second grid G in symmetrical, spacedrelationship to the line 11-11 on which apertures g g and g23 arearranged, and pieces 14 are integrally attached to the second grid G attheir conductor layers 15, as by brazing. The grid members G G and Gbridge the space between insulator pieces 14 and are secured, as bybrazing to the conductive layers M M and M provided on the insulatorpieces.

FIG. 13 shows, by way of example, a single electron gun A according tothe present invention applied to a chromatron type color picture tube.The electron gun A comprises three electrically separated cathodes K Kand K to which red, green" and blue video signals are respectivelysupplied. The three cathodes are arranged with their electron emittingsurfaces in a straight line so as to be aligned with similarly arrangedapertures g g and g in a plate-like grid (3;. A second cup-shaped grid6; has an end plate disposed adjacent grid G, and formed with threeapertures g g and g which are respectively aligned with apertures g gand g As in the previously described embodiment, electron gun A haselectrodes G G and 6,; arranged successively to define the auxiliarylens L and the main lens L.

Voltages based on the cathode voltages which are equal to thosedescribed above with reference to FIG. 9 are applied to the grids G andG and the electrodes G G and G of the gun A. Thus, beams B 13 and Bemanating from the cathodes K K and K are made to pass through aperturesg g and g of the first grid G and apertures g g and g of the second grid6;, and then through the auxiliary lens L by which the beams are made tocross each other at the optical center of the main lens L. The beams Band B emerge from main lens L along divergent paths. As in thepreviously described embodiment, convergence deflector means Fcomprising deflectors F and F formed by shielding plates P and P anddeflecting plates Q and Q are along the paths of the three beams B B andB from the main lens L. The three beams B B and B after being acted uponby the convergence deflector means F, impinge on a color screen S,comprised of sets of "red, green and blue phosphor stripes S S and Ssuccessively arranged on a face plate FP, after passing through aperforated electrode or shadow mask G provided in front of color screenS and having a medium high voltage V applied thereto. Voltages V and Vapplied across the electrode plates P and Q and across the plates P andQ of convergence deflector means F are selected so that the three beamsB B and B are made to cross each other at the position of the mask G andthus made to land only on the corresponding phosphor stripes S S and SIn this case, of course, the beams B B and B while converging at themask G are focused on the screen S.

The usual horizontal and vertical deflection means, as indicated by theyoke D, are provided for horizontally and vertically scanning the threebeams simultaneously with respect to the screen S as in the conventionalpicture tube.

Thus, by supplying red, green and blue" color video signals between thecathodes K K and K and the grip 0 respectively, the three beams B B andB are intensity-modulated, whereby a color picture is produced on thecolor screen.

Although the convergence deflection means F described above inconnection with the electron gun of each of P163. 9 and 13 is of theelectrostatic type, it is to be understood that each such deflectionmeans F of the electrostatic type may be replaced by one of a magnetictype for example, as illustrated on FIGS. 14A and B. Such deflectionmeans F of the magnetic type is shown to comprise a magnetic shieldmember 16 which may be in the form of a tube of rectangularcross-section arranged axially after the electrode G (which is not shownon FIG. 14A) so as to permit the passage therethrough of the center beamB (FIG. 9) or B (FIG. 13). Extending from one side 16a of shield member16 are two magnetic plates 17a and 17b which are in opposing, spacedrelation to each other so as to permit the passage therebetween of thebeam B or B and a similar pair of magnetic plates 18a and 18b extendfrom the other side 16b of shield member 16 to permit the passagetherebetween of the third beam B or B The edge portions of the plates17a and 17b and of the plates 18a and 18b which are adjacent the shieldmember 16 are preferably bent so as to converge toward each other in thedirection toward member 16, as particularly shown on FIG. 14B. Further,the outer edge portions 19a and 19b of the plates 17a and 17b arepreferably bent outwardly away from each other to extend along the innerwall surface of the neck portion of the tube envelope indicated at N onFIG. 14B. The outer edge portions of plates 18a and 18b are similarlybent away from each other, as at 20a. and 20b. Such bent outer edgeportions 19a, 19b, 20a and 20b form magnetic poles. Provided at theoutside of the tube neck N are electromagnetics 21 and 22 respectivelyincluding windings 23 and 24 on cores 25 and 26. The core 25 hasmagnetic pole portions 25a and 25b disposed in opposing relation topoles 19a and 19b, respectively, and the core 26 similarly has poleportions 26a and 26b in opposing relation to poles 20a and 20b,respectively.

With the above described arrangrnent, the three beams B B and B whichhave been made to cross each other at the optical center of the mainlens L and then emerge from the electrode G respectively pass betweenthe 0pposing magnetic plates 17a and 17b, through the shield member 16and between the opposing magnetic plates 18a and 18b. The beam B is notdeflected since it is shielded from the external magnetic field by themember 16, while the side beams B and B are deflected by reason of themagnetic flux distributions between the magnetic plates 17a and 17b andbetween the plates 18a and 18b which result from static convergencecurrent flow through the electromagnets 21 and 22, whereby the threebeams B B, and B are made to converge as desired, either at a point onthe phosphor screen or on the shadow mask in front of the latter. Ofcourse, it is possible to superimpose dynamic convergence currents onthe static convergent currents flowing through the electromagnets 21 and22 so that, in that case, separate dynamic convergence is not required.

Due to the fact that the inner edge portions of magnetic plates 17a, 17band 18a, 18b adjacent the sides 16a and 16b of shield member 16 areconvergent or inwardly bent, as shown in FIG. 143, the beams are made tocome very close to each other, that is, they are made to come very closeto the magnetic shield member 16 so that it is possible to effectivelyprevent disturbance of the magnetic field at the positions of the beamsB and B by the magnetic fiux passing from the magnetic plates 17a, 17b,18a, 18b to the magnetic shield member 16. Thus, it is possible toeffectively prevent distortion of the beam spots on the phosphor screen.If the distance between the opposing magnetic plates is a, the length ofthe bent portion of each magnetic plate is c, the distance between thefree edges of the converging bent inner portions is b, and therelatively small dimension of the rectangular crosssection of themagnetic shield member is d, the best results have been attained whenb/a=0.625, d/2a=c/a =0.32S and the angle between the inner edge bentportions is in the range of 30 to 60. If the inner edge portions of themagnetic plates adjacent the sides of the magnetic shield member 16 arenot bent, the magnetic field is nonuniformly distributed by reason ofthe fact that the magnetic flux at the positions of the beams B and B,is curved under the influence of the magnetic flux passing from themagnetic plates 17a, 17b and 18a, 18b toward the magnetic shield member16. The distorting effect of such non-uniform magnetic field becomesgreat especially when the distance between the adjacent beams is reducedso that the beams are made to come close to the side surfaces of themagnetic shield member 16. Such distorting effect can be effectivelyavoided by bending the magnetic plates as described above.

It will be readily apparent that, if desired, the convergenceelectromagnets 21 and 22 can be replaced by permanent magnets.

In the foregoing, electron guns embodying this invention have beendescribed as being applied specifically to color picture tubes in whicha single gun is employed to prod ce three electron beams which areintensity modulated with the usual red," green and blue color signals.However, it is obvious that an electron gun in accordance with thisinvention can be used in any other cathode ray tube requiring aplurality of beams which are to be focused at a common spot or atseparate spots on an electron-receiving screen.

Although illustrative embodiments of electron guns according to thisinvention have been described in detail herein with reference to theaccompanying drawings, it is to be understood that the invention is notlimited to those precise embodiments, and that various changes andmodifications may be made therein by one skilled in the art withoutdeparting from the scope or spirit of the invention as defined in theappended claims.

What is claimed is:

1. In a cathode ray tube having an electron-receiving screen and abeam-selecting structure adjacent said screen, a single electron guncomprising beam producing means directing a plurality of electron beamstoward said screen, means to cause said beams to intersect each other ata single point in said tube intermediate said beam producing means andsaid beam-selecting structure [screen], and main focusing lens meanscommon to all of said beams and being arranged in the paths of the beams[to focus the latter] for final focusing of each of said beamssubstantially on said screen, said main focusing lens means having anoptical center and being located to dispose said optical centersubstantially at said point at which the beams intersect, thereby toavoid the effects of coma and spherical aberration at said screen.

2. Apparatus for the reproduction of images in color, comprising anelectron receiving screen, a beam-selecting structure adjacent saidscreen, an electron gun, said electron gun having means for generating aplurality of electron beams directed toward said screen, means formodulating said electron beams with color video signals, means to causesaid electron beams to intersect each other at a single location betweensaid electron beam generating means and said beam-selecting structure[receiving screen], main focusing lens means [positioned to focus]common to all of said beams for final focusing of said beamssubstantially on said screen, and said main focusing lens means havingan optical center and being positioned to dispose the optical centerthereof substantially at said location at which the electron beamsintersect.

3. An electron gun for use in a cathode ray tube having a receivingscreen and a beam-selecting structure adjacent said screen, said guncomprising beam generating means for producing a plurality of electronbeams, means to cause said beams to intersect each other at a singlelocation intermediate said beam generating means and said beam-selectingstructure, main focusing lens means common to all of said beams[positioned] to finally focus said beams substantially on said screen,said main focusing lens means having an optical center, and said mainfocusing lens means being positioned to dispose the optical centerthereof substantially at [the] said location at which said beamsintersect whereby the effects of certain optical aberrations arediminished at said screen.

4. An electron gun for use in a cathode ray tube, said gun comprisingbeam generating means for producing a plurality of electron beams, meansto cause said beams to intersect each other substantially at a commonsingle location which is spaced from said beam generating means, mainfocusing lens means operative to finally focus said beams in a planespaced from said location at which said beams intersect, said mainfocusing lens means having an optical center, and said main focusinglens means being positioned to dispose the optical center thereofsubstantially at the location at which said beams intersect whereby theeffects of certain optical aberrations are diminished at said plane.

5. A cathode ray tube comprising beam producing means for producing aplurality of electron beams, a receiving screen positioned to have saidbeams impinge thereon, a beam-selecting structure adjacent said screen,means to cause said beams to intersect each other at a single locationin said tube between said beam producing means and said beam-selectingstructure [screen], main focusing lens means [positioned to focus]common to all of said beams for final focusing of the lattersubstantially on said screen, said main focusing lens means having anoptical center, and said main focusing lens means being positioned todispose the optical center thereof substantially at the location atwhich said beams intersect whereby the effects of certain opticalaberrations are diminished at said screen.

6. A cathode ray tube according to claim 5, in which said main focusinglens means includes a plurality of electrodes at different electricalpotentials to establish an electron lens field for said final focusingof the beams passing therethrough.

7. A cathode ray tube according to claim 5, in which said beam producingmeans includes individual beam sources, and said means to cause saidbeams to intersect each other at said location supports said individualbeam sources with the beams issuing therefrom converging to saidlocation,

8. A cathode ray tube according to claim 5, in which said beams issuesubstantially parallel to each other from said beam producing means, andsaid means to cause the beams to intersect at said location of theoptical center 1 1 includes auxiliary lens means disposed between saidbeam producing means and said focusing lens means and causingconvergence of the beams to said location.

9. A cathode ray tube according to claim 8, in which said auxiliary lensmeans includes electrodes at different electrical potentials toestablish an electron lens field through which the beams pass for saidconvergence at said location.

[ll]. A cathode ray tube according to claim 5, in which deflection meansare located between said focusing lens means and said screen to deflectthose beams which emerge from said focusing lens means along divergentpaths whereby to cause convergence of said beams at a common area onsaid screen] 11. A cathode ray tube according to claim [10,] 5 in whichsaid screen includes sets of diflerent color phosphors and saidbeam-selecting structure is [a phosphor screen member and] a perforatedshadow mask in front of said [phosphor] screen [member], [and] in whichsaid lens means focuses all of said beams at said [phosphor] screen[member], and in which deflection means are located between said mainfocusing lens means and said shadow mask to deflect those beams whichemerge from said main focusing lens means along divergent paths and saiddeflection means converges all of said beams to a common location atsaid shadow mask.

12. A cathode ray tube according to claim 5 in which deflection meansare located between said main focusing lens means and saidbeam-selecting structure to deflect those beams which emerge from saidmain focusing lens means along divergent paths whereby to causeconvergence of said beams at a common area of said beamselectingstructure, and in which said deflection means includes spaced plates atdifferent electrical potentials disposed at opposite sides of each ofsaid divergent paths to electrostatically deflect the beam in therespective path.

13. A cathode ray tube according to claim 5 [10], in which deflectionmeans are located between said main focusing lens means and saidbeam-selecting structure to deflect those beams which emerge from saidmain focusing lens means along divergent paths whereby to causeconvergence of said beams at a common area 07 said beam-selectingstructure, and in which said deflection means includes meansestablishing a magnetic field across each of said divergent paths tomagnetically deflect the beam in the respective path.

14. A cathode ray tube according to claim 5 [10], in which said beamproducing means defines sources for three of said beams, with one ofsaid sources being at the optical axis of said main focusing lens meansand the other two sources being equally spaced from said one source atopposite sides of the latter on a straight line extending diametricallyacross said optical axis so that only the beams from said other twosources follow divergent paths upon emerging from said focusing lensmeans, and in which deflection means are located between said mainfocusing lens means and said beam-seiecting structure to deflect thosebeams which emerge from said main focusing lens means along saiddivergent paths whereby to cause convergence of said beams at a commonarea of said beam selecting structure.

15. A cathode ray tube according to claim 14, in which said deflectionmeans includes a pair of first plates at equal electrical potentialdisposed at opposite sides of said optical axis for the passagetherebetween of the beam from said one source upon emergence thereoffrom said main focusing lens means, and second plates spaced outwardlyfrom said first plates for the passage between said first and secondplates of said beams from said other two sources, said second platesbeing at an electrical potential different from that of the first platesto electrostatically deflect the respective beams from said other twosources in the direction toward said optical axis.

16. A cathode ray tube according to claim 14, in which said deflectionmeans includes a tubular mangetic shield arranged along said opticalaxis for the passage therethrough of the beam from said one source uponemergence from said main focusing lens means, pairs of spaced magneticplates extending outwardly from opposed sides of said shield for thepassage between said pairs of plates of the beams from said other twosources, and magnet means operatively associated with said pairs ofplates to establish, between the plates of each pair, a magnetic fieldfor deflecting the beam passing therethrough toward said optical axis.

17. A cathode ray tube according to claim 16, in which the plates ofeach of said pairs have inner edge portions which converge toward eachother in the direction toward the adjacent side of said shield forminimizing distortion of the respective beams by non-uniformity of themagnetic field between said plates.

18. A cathode ray tube according to claim 5, in which said beamproducing means includes cathode means emitting electrons, and first andsecond grid means arranged successively in adjacent, opposing relationto said cathode means and to each other, respectively, and havingaligned apertures for each of said beams to form the latter parallel toeach other.

19. A cathode ray tube according to claim 18, in which said second gridmeans is in the form of a single plate having all of the respectiveapertures therein, said main focusing lens means includes a plurality oftubular electrodes arranged successively in order after said second gridmeans and being at different electrical potentials to establish anelectron lens field for the final focusing of all of the beams passingtherethrough, and said means to cause the beams to intersect at saidlocation includes an annular side wall extending from the periphery ofsaid plate of the second grid means and being at an electrical potentialdifferent from that of the next adjacent electrode of said main focusinglens means to establish an auxiliary electron lens field for convergingthe beams formed in parallel relation to each other.

20. A cathode ray tube according to claim 18, in which said cathodemeans includes a single cathode member having an electron emittingsurface, said first grid means includes a plurality of grid members eachcorresponding to one of said beams and having a respective aperturetherein, said grid members of the first grid means being disposed inconfronting, adjacent relation to said electron emitting surface, saidsecond grid means includes a single plate in confronting, adjacentrelation to said members of the first grid means, and insulating andspacing members are interposed between, and bonded to said grid membersof the first grid means and said plate for maintaining predeterminedrelative spacing and alignment of said apertures in the first and secondgrid means.

21. An electron gun for use in a cathode ray tube, said gun comprisingbeam generating means for producing a plurality of electron beams, meansto cause said beams to intersect each other at a single location spacedfrom said beam genearting means, main focusing lens means [positioned tofocus] for the final focusing of said beams, said main focusing lensmeans being formed by a plurality of electrical elements and having anoptical center, said optical center being located along the axis of saidmain focusing lens means where the eflects of optical aberrations aresubstantially a minimum, and said focusing lens means being positionedto dispose the optical center thereof substantially at [the] saidlocation at which said beams intersect whereby the effects of certainoptical aberrations in the focused beams are diminished.

22. An electron gun in accordance with claim 21 in which said beamgenerating means includes one cathode for emitting electrons and atleast two grid members positioned in opposing relationship to theelectron emitting surface of said cathode.

23. An electron gun in accordance with claim 21 in which said[individual] electron beams as generated by said beam genearting meanseach has [have] a cross-sec- 13 tional areas less than thecross-sectional area thereof at the optical center of said main focusinglens means where said beams intersect.

24. An electron gun according to claim 21, having deflection means fordeflecting those beams which emerge from said main focusing lens meansalong paths diverging from the optical axis of said main focusing lensmeans to cause convergence [for] of all of said beams in a commonlocation beyond said gun.

25. An electron gun in accordance with claim 24 in which said beamproducing means includes cathode means emitting electrons, and first andsecond tubular grid means arranged successively in adjacent, opposingrelation to said cathode means and to each other respectively and havingaligned apertures for each of said beams to form the latter parallel toeach other.

26. An electron gun in accordance with claim 21 in which said mainfocusing lens means includes a plurality of electrodes at differentelectrical potentials to establish an electron lens field therebetweenfor said final focusing of the beams passing therethrough.

27. An electron gun in accordance with claim 26 in which said electrodesof said main focusing lens means [further] include [includes] at leasttwo tubular electrodes arranged in successive order with said electronlens field being established therebetween.

28. An electron gun in accordance with claim 27 in which said beamsissue substantially parallel to each other from said beam producingmeans, and said means to cause the beams to intersect includes auxiliarylens means disposed between said beam producing means and said mainfocusing lens means.

29. An electron gun in accordance with claim 28 in which said auxiliaryleans means includes at least two tubular electrodes at ditferentelectrical potentials to establish an electron lens field through whichthe beams pass for convergence.

30. An electron gun in accordance with claim 21 in which said means tocause the beams to intersect includes beam generating means arranged onan arcuate surface whereby said beams issue from said beam generatingmeans in a manner to intersect substantially [substantively] at theoptical center of said main focusing lens means.

31. An electron gun in accordance with claim 30 in which the center ofsaid arcuate surface is on the same axis as the optical center of saidmain focusing lens means.

32. An electron gun in accordance with claim 21 in which said beamgenerating means includes at least two cathodes for emitting electronsand one grid member positioned in opposing relationship to the electronemitting surfaces of said cathodes.

33. An electron gun in accordance with claim 32 in which said cathodesare arranged in a straight line and aligned with apertures provided insaid grid member.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 3,596,126 7/1971 Yoshida et al. 313-86 2,679,6145/1954 Friend 315-13 2,690,517 9/1954 Nicoll et al. 313- 2,711,4936/1955 Lawrence 313-70 X 2,862,144 11/1958 McNaney 313-69 X 2,887,5985/1959 Benway 313-70 3,011,090 11/1961 Moodey 313-70 X 3,325,675 6/1967Sanford 315-13 3,363,128 1/1968 De France et al 313-77 r ROBERT SEGAL,Primary Examiner 0 US. Cl. X.R. 315-16

